1. Field of the Invention
The present invention relates to methods and related communications devices utilized in re-establishing a receiving side in a wireless communications system, and more particularly, to a method and related apparatus for handling control PDUs when only the receiving side of an RLC entity is re-established.
2. Description of the Prior Art
The third generation (3G) mobile communications system has adopted a Wideband Code Division Multiple Access (WCDMA) wireless air interface access method for a cellular network. WCDMA can provide high frequency spectrum utilization, universal coverage, and high quality, high speed multimedia data transmission. The WCDMA method also meets all kinds of QoS requirements simultaneously, providing diverse flexible two-way transmission services and better communication quality to reduce transmission interruption rates.
Taking a signal communications protocol standard set forth by the 3rd Generation Partnership Project (3GPP) as an example, targeting the Access Stratum (AS), the 3G mobile communications system defines various protocol stacks, such as Radio Resource Control (RRC), Radio Link Control (RLC), Media Access Control (MAC), Packet Data Convergence Protocol (PDCP), and Broadcast/Multicast Control (BMC). In addition, the 3G mobile communications system also provides different levels of transmission quality, and can operate in different corresponding modes according to different transmission quality requirements, such as: Transparent Mode (TM), Unacknowledged Mode (UM), and Acknowledged Mode (AM). TM is appropriate for use in services with high requirements for real-time transmission, UM is appropriate for use in services with requirements for real-time transmission and packet sequencing, and AM is appropriate for use in services with low requirements for real-time transmission, but high requirements for data accuracy.
In AM, the RLC layer combines a transmitting side and a receiving side. The transmitting side and the receiving side each process transmission and reception through the RLC layer, and both sides can share system resources. In some circumstances, the RLC layer must be reestablished, e.g. when changing the size of a protocol data unit. The prior art reestablishes the RLC layer by reestablishing the transmitting side or the receiving side.
Directed at operations corresponding to reestablishing the RLC layer, a communications protocol specification established by the 3GPP (3GPP TS 25.322 V6.4.0 (2005-06), “Radio Link Control (RLC) protocol specification (Release 6)”) and a Change Request (R2-052168 “Single Sided RLC Re-establishment”, Motorola, 3GPP RAN2 #48 meeting, August 2005) are already described in detail. The details of the communications protocol specification and the Change Request can be summarized as follows: When reestablishment of a transmitting side and/or a receiving side of an AM RLC entity is initiated by an upper layer, the RLC entity should execute the following two operations:    1. If the receiving side of the RLC entity is being reestablished, reset state variables (VR(R), VR(H), and VR(MR)) corresponding to a receiver; set configurable protocol parameters (Configured_Tx_Window_Size and Configured_Rx_Window_Size) corresponding to the receiver to accurate values; set a Hyper Frame Number of the receiving side (downlink of the receiver) to a value set by the upper layer; and discard all control PDUs of the receiving side and the transmitting side, and discard data PDUs of the receiving side. If only the receiving side is being reestablished, the prior arts described above have not yet disclosed a method of handling a timer.    2. If the transmitting side of the RLC entity is being reestablished, reset state variables (VT(S), VT(A), VT(DAT), VT(MS), VT(PDU), VT(SDU), VT(RST), VT(MRW), and VT(WS)) corresponding to a transmitter; set configurable protocol parameters (MaxDat, Poll_PDU, Poll_SDU, Poll_Window, MaxRST, MaxMRW, OSD_Window_Size, and DAR_Window_Size) corresponding to the transmitter to accurate values; set a Hyper Frame Number of the transmitting side (uplink of the receiver) to a value set by the upper layer. In this operation, if only the transmitting side of the RLC entity is being reestablished, discard all control PDUs of both the receiving side and the transmitting side, and discard all already successfully transmitted SDUs of the transmitting end. Segment any not yet discarded SDUs into PDUs again based on a configured size of the PDU. If the transmitting side and the receiving side of the RLC entity are both being reestablished, discard the control PDUs of the receiving side and the transmitting side, and discard the data PDUs of the receiving side. If the transmitting side is being reestablished, regardless of whether or not the receiving side is being reestablished, stop all timers except for Timer_Poll_Periodic, Timer_Status_Periodic, and Timer_Discard, which corresponds to the SDUs that have not yet been discarded. Finally, if needed, inform the upper layer of the SDUs that have already been discarded.
When only the receiving side is being reestablished, the prior art discards all of the control PDUs of the receiving side and the transmitting side, which may cause an error in operation of the system. For example, a Move Receiving Window Super-Field (MRW SUFI) PDU of an SDU discard command has already been transmitted before the receiving side is reestablished, but has been lost in the transmission process, because the prior art discards all of the control PDUs when only the receiving side is being reestablished, the MRW SUFI PDU cannot be retransmitted, such that the SDU discard process cannot be accurately executed in the transmitting side. Likewise, if the RLC layer reset process has already been initiated in the transmitting side before the receiving side is reestablished, but the RESET PDU has been lost in a transmission process, because the prior art discards all of the control PDUs when only the receiving side is being reestablished, including the RESET PDU, the RESET PDU cannot be retransmitted, and the reset process cannot be executed smoothly.